Pressure Harvesting - from ocean depths

[DaveC426913]

so a hose attached to the Variable volume pressure vessel down at depth, with say 35000kPa of pressure inside it would not provide 35000Kpa at the surface?

Yes. Once. And only because you energized the system first. If you want it to do so a second time, you will have to re-energize it.

A rock lifted to the top of a cliff can be used to pressurize air. Once.
If you want to reuse it, you will have to lift it back to the top of the cliff.
And that will cost you more energy than simply compressing the can in the first place.

Please, for the love of all that is holy, take a moment to ruminate on this.

 

[billvon]

Deep ocean pressure can be exploited for potential energy.

Yep. And a rock on the top of a crane can be exploited for potential energy as well. Once you carry it up there, that is.

 

[DaveC426913]

Dave this is quite funny because you seem to be mixing me up with QQ.

Was I?

I thought you were posting a scenario that you intuited didn't make sense but couldn't spot the error. Maybe your post was deliberately facetious and it went over my head.

My concern was that, by setting up a scenario (one that was flawed to begin with) it might set QQ going down another unnecessary rabbit hole.

 

[Write4U]

Before we start dismissing novel ideas out of hand, lets examine current technology and research.

Using Water Pressure at the Bottom of the Ocean to Store Energy

Rainer Schramm, inventor and founder of the company Subhydro AS said, “Imagine opening a hatch in a submarine under water. The water will flow into the submarine with enormous force. It is precisely this energy potential we want to utilize. Many people have launched the idea of storing energy by exploiting the pressure at the seabed, but we are the first in the world to apply a specific patent-pending technology to make this possible.”

Related article: Fuel Efficiency Boosted by New HydraGen Technology

To use the water pressure at the seabed in practice, the mechanical energy is converted by a reversible pump turbine, as in a normal pumped storage hydroelectric plant.

Schramm explains, “A pumped storage power plant is a hydroelectric plant that can be “charged” up again by pumping the water back to the upper reservoir once it has passed through a turbine. This type of power plant is used as a “battery”, when connected to the power grid.”

In this pumped storage power plant a turbine will be connected to a tank on the seabed at a depth of 400-800 meters. The turbine is fitted with a valve, and when this is opened, water flows in and starts turning the turbine. The turbine drives a generator to produce electricity. One can connect as many tanks as one might wish. In other words, it is the number of water tanks that decides how long the plant can generate electricity, before the energy storage capacity is exhausted.

https://oilprice.com/Energy/Energy-...-the-Bottom-of-the-Ocean-to-Store-Energy.html

As I undestand it this is not used for constant use, it is not efficient enough for this ,but is a natural storage of energy in case of shortage. The additionl energy for the pumps can be fed from excess wind mills piped down to power the pumps until presure tank is empty. Then, when needed the tank is opened and the inrushing water provides the kinetic power to generate electicity.

The main point is that nothing but electricity goes up and down. The power is generated at the ocean bottom.

If the Germans are involved, there has to be something promising to this system. They usually don't fool around with useless technology.

 

[exchemist]

Was I?

I thought you were posting a scenario that you intuited didn't make sense but couldn't spot the error. Maybe your post was deliberately facetious and it went over my head.

My concern was that, by setting up a scenario (one that was flawed to begin with) it might set QQ going down another unnecessary rabbit hole.

Ah OK. No I was serious.

But I want to know the flaw in the scenario, if you've found it, because I could not see it, although it did seem to give a strange answer. Can you explain where the flaw is?

 

[DaveC426913]

Ah OK. No I was serious.

But I want to know the flaw in the scenario, if you've found it, because I could not see it, although it did seem to give a strange answer. Can you explain where the flaw is?

I started one there. Can you build a box that has the same volume and weight as water, and is full of a compressible fluid? Does your experiment still work with that box?

 

[exchemist]

I started one there. Can you build a box that has the same volume and weight as water, and is full of a compressible fluid? Does your experiment still work with that box?

You can buy 1 litre steel water bottles. I envisage something like that, capable of withstanding 10bar and weighing 1kg, and with a valve on it that QQ can open remotely. You start with air in it at atmospheric pressure, close the valve and drop it in the water.

It's only thought experiment, after all.

Is there a flaw in this?

 

[DaveC426913]

You can buy 1 litre steel water bottles. I envisage something like that, capable of withstanding 10bar and weighing 1kg, and with a valve on it that QQ can open remotely. You start with air in it at atmospheric pressure, close the valve and drop it in the water.

It's only thought experiment, after all.

Is there a flaw in this?

OK, I haven't examined it in detail. but a few things raise flags that invite further analysis:

I imagine a simple scenario with a 1 litre container weighing 1kg, so its buoyancy exactly matches its weight. This can descend, without any work being done at all, say to 100m depth,

Is this the case? Is a hollow container full of air the same volume at the surface as it is at 100m? Trying to remember if this is a factor from my Scuba days.

The work done by the water to compress it is given by W=nRTln(V0/V) which I work out to be about 230J*. This is then the stored energy QQ can "harvest" when it gets back to the surface.

If you say so.

However the volume of water displaced by this device is now only 0.1litres, so its apparent "weight" is now 0.9kg, i.e. 9N.

Walk me through this. How did you figure out its apparent weight if we haven't even figured out how much of the 1kg is steel and how much is air?

So to pull it up to the surface one has to expend 9x100 = 900J. Nearly 4 times the stored energy. But I can't think where in the energy balance for this operation, the rest appears. So I'm wondering if I have made an error somewhere. Any ideas?

Again, can you simply assume a given object is neutrally buoyant everywhere in the water column?

 

[Write4U]

I started one there. Can you build a box that has the same volume and weight as water, and is full of a compressible fluid? Does your experiment still work with that box?

There is no compression involved at all. Vacuum is involved and the kinetic force of water inflow is used to generate electricity directly via turbine generators.

As long as the box remains anchored at the sea bottom you can perform the inflow and and out-pumping of water thereby generating electricity and requiring only two electrical cables to the surface. Nothing needs to be hauled up or down, the generating process is entirely at the sea floor. Only electricity is transported.

They use the system used by submarines but for purposes of generating electricity, not for buoyancy.

It is not a replacement for mass energy production. It is an energy storage system, in case it is needed.
The point is that the German firm has a patent on the system which means it is functional and that is what we are discussing, no?

 

[Write4U]

Yep. And a rock on the top of a crane can be exploited for potential energy as well. Once you carry it up there, that is.

You are looking at this from a completely wrong perspective. Nothing needs to be hauled up or down or compressed.

On the contrary, it is vacuum and "flooding the vacuum chambers with water under enormous pressure past electric generators, which produces the electricity, until the vacuum is filled, at which time the turbines are reversed and the water is pumped back out, until vacuum is reached and ready to be flooded again. The illustration shows an airpipe that helps in pumping out the water without creating too great a vacuum which might collapse the vacuum chambers. As the water rushes in it will push the air out at the surface and replace the air with water. And the cycle starts all over again.

The system is used succesfully by submarines for buoancy. But there is no reason why it cannot be used for generating electricity. How Submarines Work

To control its buoyancy, the submarine has ballast tanks and auxiliary, or trim tanks, that can be alternately filled with water or air (see animation below). When the submarine is on the surface, the ballast tanks are filled with air and the submarine's overall density is less than that of the surrounding water. As the submarine dives, the ballast tanks are flooded with water and the air in the ballast tanks is vented from the submarine until its overall density is greater than the surrounding water and the submarine begins to sink (negative buoyancy). A supply of compressed air is maintained aboard the submarine in air flasks for life support and for use with the ballast tanks.

https://science.howstuffworks.com/transport/engines-equipment/submarine1.htm

 

[DaveC426913]

There is no compression involved at all. Vacuum is involved and the kinetic force of water inflow is used to generate electricity directly via turbine generators.

Sorry, I think you may be conflating multiple things. What I am responding to is a very simple thought experiment setup by Exchemist back in post 96.

As long as the box remains anchored at the sea bottom you can perform the inflow and and out-pumping of water thereby generating electricity and requiring only two electrical cables to the surface. Nothing needs to be hauled up or down, the generating process is entirely at the sea floor. Only electricity is transported.

Which seems to be completely unrelated to Ex's contraption.

The point is that the German firm has a patent on the system which means it is functional and that is what we are discussing, no?

Hopefully, no one doubts that oceans and many other things can be used to store and then retrieve energy - like a battery.

That is a simple as lugging a rock to the top of a cliff and leaving it there until you need some Oomph to crack your mussels. The rock is a battery or storing energy that can be used as-needed.
But you cannot harvest energy from it.

 

[DaveC426913]

You are looking at this from a completely wrong perspective. Nothing needs to be hauled up or down or compressed.
On the contrary, it is vacuum and "flooding the vacuum chambers with water under enormous pressure past electric generators, which produces the electricity, until the vacuum is filled, at which time the turbines are reversed and the water is pumped back out, until vacuum is reached and ready to be flooded again. The illustration shows an airpipe that helps in pumping out the water.

No.

QQ is trying to harvest energy.
Your system does not harvest any energy; it simply stores energy put into it.

Your intent is good, but it is a red herring that is clouding the issue at the heart of QQ's thread.

 

[Write4U]

No.

QQ is trying to harvest energy.
Your system does not harvest any energy; it simply stores energy put into it.

Your intent is good, but it is a red herring that is clouding the issue at the heart of QQ's thread.

I thought the idea was to generate power by any means using the ocean's water pressure, which this does and does not involve raising and lowering anything, which is what you are concentrating your falsification on.

Ask QQ, if he is picky about the actual formula used to achieve the intended goal.

We can just change the OP to read "Vacuum Harvesting from ocean depths"

 

[Write4U]

But you cannot harvest energy from it.

Yes you can, this is not a one time process. It can be used indefinitely perhaps even on its own power or with minimal power assistance from the surface.
Submarines use it constantly. Your rock on a hill is the "red herring" in this example of harvesting energy from ocean pressure.

I look for utility not for theoretical curiosities. Have you not debunked that yet?

 

[DaveC426913]

I thought the idea was to generate power

The device you describe does not generate power. It stores power.


Look, here:

"flooding the vacuum chambers with water under enormous pressure past electric generators, which produces the electricity, until the vacuum is filled, at which time the turbines are reversed and the water is pumped back out, until vacuum is reached

Yep. The water is pumped back out.

Which takes energy input.

Guess how much? More than you gained.

It's a battery, not a generator.

 

[billvon]

You are looking at this from a completely wrong perspective. Nothing needs to be hauled up or down or compressed.

Of course it does.

On the contrary, it is vacuum and "flooding the vacuum chambers with water under enormous pressure past electric generators, which produces the electricity, until the vacuum is filled, at which time the turbines are reversed and the water is pumped back out, until vacuum is reached and ready to be flooded again. The illustration shows an airpipe that helps in pumping out the water without creating too great a vacuum which might collapse the vacuum chambers. As the water rushes in it will push the air out at the surface and replace the air with water. And the cycle starts all over again.

A lot of mistakes there.

First you have to get the empty chambers down there, which would be pretty hard if they are large. So most likely they are sent to the bottom partially or completely flooded, so that they sink. Then they have to be pumped out, with the water replaced by air (not vacuum.) Then they can be used for energy generation, until the tanks are full of water.

The airpipe is to provide surface pressure to the tanks, so they see a low pressure. The pumps at the bottom then pump out the water. A pump at the top cannot physically pump the water of a deep well.

The system is used succesfully by submarines for buoancy. But there is no reason why it cannot be used for generating electricity.

Because it requires a lot of energy (in the form of compressed air or pumps) to cause a submarine to rise.

 

[billvon]

Yes you can, this is not a one time process. It can be used indefinitely . . . .

As long as you provide the power to pump the chambers back out.

Your rock on a hill is the "red herring" in this example of harvesting energy from ocean pressure.

It is exactly the same. You can use a hoist to allow the rock to descend, thus harvesting energy from gravity. And it can be used indefinitely - as long as you provide the energy to haul it back up again. There is also an energy storage system (NOT an energy generation system) that uses the "haul rocks to the top of a crane" method.

 

[exchemist]

OK, I haven't examined it in detail. but a few things raise flags that invite further analysis:


Is this the case? Is a hollow container full of air the same volume at the surface as it is at 100m? Trying to remember if this is a factor from my Scuba days.



If you say so.


Walk me through this. How did you figure out its apparent weight if we haven't even figured out how much of the 1kg is steel and how much is air?


Again, can you simply assume a given object is neutrally buoyant everywhere in the water column?

A steel cylinder may compress very slightly I suppose at 100m down, if the air within is only 1 bar, but this will be negligible, assuming it does not collapse. If for simplicity we treat both the cylinder and the water as incompressible, which they both very nearly are, then the buoyancy will not change with depth.

The apparent weight is the weight of the object minus the buoyancy. If the cylinder is 1kg then the weight is 10N approx. (The mass of a mole of air is ~29g and at ntp this occupies 24litres. So 1 litre of air at ntp has a mass of ~ 1gram, i.e. negligible.) If the cylinder displaces 1 litre of water, then the buoyancy force is the weight of 1 litre of water, i.e. the weight of 1kg, i.e. 10N.

That's why I chose a volume of 1 litre and a mass of 1kg, so the forces would cancel and we would not have to worry about any work done as the cylinder sinks. So we have a cylinder with neutral buoyancy (just like a well-trimmed submarine in fact) sinking slowly to 100m depth.

 

[billvon]

You are looking at this from a completely wrong perspective. Nothing needs to be hauled up or down or compressed.

Water does.

On the contrary, it is vacuum and "flooding the vacuum chambers with water under enormous pressure past electric generators, which produces the electricity, until the vacuum is filled, at which time the turbines are reversed and the water is pumped back out, until vacuum is reached and ready to be flooded again.

Exactly. Energy comes out, energy goes in. You always need more energy in than you get out. There's no way around that. It is storage, not harvesting.

The illustration shows an airpipe that helps in pumping out the water without creating too great a vacuum which might collapse the vacuum chambers.

The airpipe does not help in pumping the water out. It simply allows surface-pressure air to flow in and out of the chamber.

(BTW no such thing as "too great a vacuum that might collapse the vacuum chambers." The difference between surface pressure and vacuum is 15psi; the difference between surface pressure and seafloor is 1200psi. If the tank can withstand 1200 psi it can withstand 1215 psi.)

As the water rushes in it will push the air out at the surface and replace the air with water.

And generate power. Then you pump it out and it takes power.

The system is used succesfully by submarines for buoancy. But there is no reason why it cannot be used for generating electricity.

And yet submarines need either nuclear reactors or batteries to provide electricity! That's because IT TAKES ENERGY to control bouyancy.

 

[Write4U]

As long as you provide the power to pump the chambers back out.

Yes. you can use the turbines used for generating the power from the inflow for pumping the water back out . Of course that will use some energy , but you can use battery storage for that which will charge again during the inflow. Th article does describe how it works and they can back up the science and the technical details.

How do submarines do it when they are sumberged for months at a time? Of course they use energy, but the system works. The rest is a matter of efficiency.

It is exactly the same. You can use a hoist to allow the rock to descend, thus harvesting energy from gravity. And it can be used indefinitely - as long as you provide the energy to haul it back up again. There is also an energy storage system (NOT an energy generation system) that uses the "haul rocks to the top of a crane" method.

Are you comparing the kinetic energy of a rock with an electric feed to a reversible electric motor/generator?
Why don't you read the links I provide. You are making a lot of false assumptions due my abbreviated version. The Germans have a patent on a functional system. Are you not interested in finding out how it works or are you gonna argue with me about it? I brought you the infomation, I am the messenger, don't ask me about the details of the message.